Referring to FIG. 1, a circuit 10 illustrates such a conventional approach for implementing a detection circuit. The circuit 10 generally comprises a number of comparators 12a-12n, a number of resistors 14a-14n, a number of capacitors 16a-16n and an inductor 18.
The circuit 10 detects signals primarily through signal peak detection. Input signals are not detected differentially, but compared the positive input transitions with an externally set common mode offset voltage. The capacitor 16n is charged when valid signals are present and discharge through a bleed resistor.
Referring to FIG. 2, a circuit 40 is shown illustrating another conventional detection circuit. The circuit 40 generally comprises a detector logic block 42, a comparator 44, a comparator 46 and a voltage offset current stealing circuit 48. The circuit 40 takes advantage of current stealing to set a trip threshold level. An offset voltage is created between the gates of a differential pair in the stealing circuit. The stealing circuit differential pair is matched to the comparator differential pair, and their drains are connected together. When the voltages at the comparator inputs are equal, the currents through them are unequal by the amount taken by the stealing circuit. A trip point threshold is reached when comparator inputs are unequal by the offset voltage at the stealing circuit. The currents into the comparator differential pair will become equal. As the comparator voltage increases beyond the offset voltage, the output state of the comparator will change.
The circuit 10 uses discrete components which can false trigger with common mode noise. The circuit 40 requires separate differential pairs to create the threshold and comparison circuits. The differential pairs are required to match (or track) each other over process and temperature variations. The currents setting the threshold could be small and difficult to control.